Hydrostatic reversible drive

ABSTRACT

A source of hydrostatic pressure is connected to a reversible hydraulic motor over a pair of pressure lines, selectively carrying high or low pressure; a controllable pressure limiting valve is connected to the lines, and having an output connected to a drain. The controllable pressure limiting valve includes a main piston operating in a piston chamber, a settable pilot valve unit, an interconnecting line connecting fluid under line pressure to the settable pilot valve unit and a drain valve unit having a movable drain control piston connecting the interconnecting line with the side of the main piston to which the higher pressure is applied, the arrangement permitting direct drain connection of either of the pressure lines to the drain with a minimum of parts or external interconnections.

United States Patent Adams Bobst May 29, 1973 HYDROSTATIC REVERSIBLEDRIVE 3,625,007 12/1971 Hemdon ..60/53 R 75 Inventor: Gerhard BobstOens' en, Switzer- 1 land mg Primary Examiner-Edgar W. GeogheganAttorney-Flynn & Frishauf [73] Assignee: Von Roll AG, Gerlafingen,Switzerv land [57] ABSTRACT [22] Filed:- June 10, 1971 A source ofhydrostatic pressure is connected to a [21] A I No 151 721 reversiblehydraulic motor over a pair of pressure pp lines, selectively carryinghigh or low pressure; a controllable pressure limiting valve isconnected to the [30] Foreign Application Priority Data lines, andhaving an output connected to a drain. The controllable pressurelimiting valve includes a main June 26, i970 Switzerland ..9735/70piston operating in a piston chamber a Settable pilot valve unit, aninterconnecting line connecting fluid 2? 3 21 under line pressure to thesettable pilot valve unit and i '6/ R 52 B a drain valve unit having amovable drain control 1 0 care piston connecting the interconnectingline with the side of the main piston to which the higher pressure is 5References Cited applied, the arrangement permitting direct drain con-UNITED STATES PATENTS nection of either of the pressure lines to thedrain with a minimum of parts or external interconnections. 2,961,829ll/l960 Weisenbach ..60/53 R 3,583,157 6/1971 ..60/53 R 12 Claims, 2Drawing Figures /'5 32 44 34 62 3'5 43 4/ $7 1 K H i 7/ 3 1 56 x. A a AO J '3 g g t t N 23 EN" mu" 1 HYDROSTATIC REVERSIBLE DRIVE The presentinvention relates to a hydrostatic reversible drive and moreparticularly to the type of drive in which a reversible hydraulic motoris connected to a pair of pressure lines which, selectively, havepressure applied thereto, the lines being additionally connected to apressure limiting valve whichconnects that one of the lines having thehigher pressure to a drain when overpressure arises.

The reversible hydraulic motor is .connectable to a pair of pressurelines which is supplied by hydraulic fluid, under pressure, over checkvalves and which are, selectively, connected to a drain valve. To limitthe pressure of the two pressure lines, a settable pressure limitingvalve is provided.

Various arrangements for hydrostatic reversible drives are known. Mostof these known arrangements require devices to limit the pressure ofboth pressure sides, since the operating pressure is applied to the one,or the other connecting line from the hydraulic pump, depending on thedesired direction of movement. In a simple cpnstruction, each pressureline has a separate pressure limiting valve, usually in the form of aslide piston valve, or a valve cooperating with a valve seat, themechanically movable part being biass ed by a predetermined force, forexample by a settable, adjustable coil spring. Using two pressurelimiting valves, that is, one for each pressure line is comparativelyexpensive, and particularly so since these valves have to be dimensionedto be sufficiently large so that the maximum fluid flow can be earriedwithout any appreciable back pressure being developed in the valve.Further, both valves must be adjusted to operate at precisely the sameover pressure, whieh is difficult to maintain in operation.

It has previously been proposed to provide pressure limiting valveswhich have pre-controlled pilot valves, which permit better control ofthe threshold pressure at which the pressure valves will operate, andfurther decreases the size of the valves themselves. Yet, two actualoperating valves are still required, one for each pressure line. Sinceonly one of the pressure lines is actually under operating pressure,only one of the two valves need ready to limit the pressure at therespective pressure side, the other one of the two valves always beinginactive. This lirnit on the utilization efficiency has given rise tothe development of pressure limiting valves in which only a single valveunit is used and reversible hydraulic drives have been proposed in whichthe pressure for both pressure lines is limited by one single valve.This arrangement, however, requires a switch-over system which alwaysinterconnects that portion of the pressure line with the single valvewhich, at any time, is under operating'pressure. Switch-over systems ofthis type can be quite simple, for example constructed utilizing a pairof oppositely directed check valves. This solution, therefore, is lessexpensive and less space consuming than using one each pressure limitingvalve for each pressure line.

Other known arrangements utilize pressure limiting valves withoutspecial S i ch-over arrangements; rather, the switch-over arrangement istransferred to the drain valve itself. This solution is based on the consideration that the drain valve is already a switch-over unit itselfwhich will drain pressure from that pressure line which has the lowerpressure arising therein. It is comparatively simple to so modify thedrain valve that it will also be able to carry out the switch-overfunction of the pressure limiting valve, that is, application of theoperating pressure to the respective pressure. limiting valve. Such amodified drain valve permits elimination of the previously. mentionedcheck valves and the total costs of the system are additionally reduced.

The last two mentioned systems have the substantial disadvantage thatthe connection between the respective pressure sides, having theoperating pressure-applied thereto, and the pressure limiting valve inthe switch-over arrangement is either in the form of check valves or inthe form of a drain valve. Both check valves, as well as drain valveshave substantial constrictions in their fluid flow, and present at leastseveral changes of fluid flow directions, so that they, effectively,form hydraulic chokes which interfere with the complete utilization ofthe flow volume of the pressure limiting valve. It has been found byexperience that a sufficiently large dimensioning of the ducts of theswitch-over arrangement, to provide sufficient fluid flow without backpressure would increase the costs to such an extent that, economically,the desiredsimplification is not achieved. In particular, the drainvalve, which is to flmction as a switch-over controller for'the pressurelimiting valve must be designed for dimensions which are much greaterthan those required by its drain function itself; the capacity of thedrain valve, for draining alone is, customarily, sufficient if the valvecan carry 10 to 15 percent of the maximum pressure flow. Such a drainvalve would thus be substantially ove'rdimensioned when it is also to beused as a switch-over device for the pressure limiting valve, so that asaving in costs and installation, in comparison to a separateswitch-over device, is quite low.

It is an object of the present invention to provide a single pressurelimiting valve in hydraulic arrangements in which there is little or nopressure drop in the switchover device between the pressure side of theline carrying the operating pressure, and the pressure limiting valve,so that a single pressure limiting valve can be used which,nevertheless, has full operating pressure applied thereto.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, a source of hydraulicfluid and a pump supply hydraulic fluid under pressure to a reversiblehydraulic motor over a pair of pressure lines, interconnecting the pumpand the reversible motor and determining the direction of movement ofthe motor and which one of the pressure lines is the high pressure andwhich the low pressure side. The pressure lines are connected to acontrollable pressure limiting valve, combined with a drain, thecontrollable pressure limiting valve limiting the pressure of the highpressure line. The controllable pressure limiting valve comprises a mainpiston and a connection interconnecting pressure from both the pressurelines to the main piston. A settable pilot valve is provided and aconnecting line providing fluid to the settable pilot valve unit. Adrain valve, having a movable drain control piston connects theinterconnecting line with the side of the main piston which has thehigher pressure applied thereto.

The connections interconnecting the pressure lines to the main piston donot include any control elements. The arrangement of the presentinvention requires only a small quantity of fluid to control thesettable pilot valve, so that the drain valve can be left in its usualsize; on the other hand, a direct connection between the pressure sideand the pressure limiting valve is provided.

Both sides of the main piston are connected to that pressure line whichcarries the higher pressure over interconnections controlled by thedrain valve control piston. This permits rapid response of the mainpiston and thus of the pressure limiting valve.

In accordance with a feature of the invention, the line which appliespressure to the pilot valve includes a choke point or constriction, sothat, when the pilot valve responds, a pressure difl'erence arises atopposite sides of the main piston, and the main piston will respondquickly.

The invention will be described by way of example with reference to theaccompanying drawings, wherein:

FIG. 1 is a simplified schematic hydraulic diagram of a hydrostaticreversible drive; and

FIG. 2 is a longitudinal cross-sectional view of a controllable pressurelimiting valve unit in which supply of pressure fluid to the pilot valveis controlled by a drain control valve.

The reversible drive of FIG. 1 comprises a pump 1, driven by a motor Mwhich additionally drives a filling or supply pump 2, having its suctionline connected to a sump or other supply or source of hydraulic fluid.Hydraulic fluid is pumped over lines 4, 5 and over check valves 6, 7 tothe two pressure sides 8, 9, the lines 8, 9 respectively forming a highpressure or low pressure side of the reversible drive, depending uponthe direction of movement of the reversible drive.

Lines 8, 9 interconnect the pump 1 with a hydraulic motor 10 having anoutput connected to a load, schematically indicated as L, which may forma drive, or machine to perform work. Motor 10 may have a rotary outputshaft. The two pressure lines 8, 9 are connected by means of connectionlines 12, 13 with a common valve block 15 which includes the pressurelimiting valve, to be described in detail below. Application of pressurefluid to the pressure limiting valve is controlled over a drain valve,connected to a drain line 16 through which the drain oil is returned tothe source, or sump 3, if necessary, over an interconnected low pressurelimiting valve, not shown, and as well known in the art. 1

The pressure limiting valve, generally indicated at 15, and shown indetail in FIG. 2, has a valve body 20 covered by end covers 21, 22secured with screws 23 to the body 20. Body 20 is formed with a bore 25in which a drain valve piston 26 is located. When in the position ofFIG. 2, the drain line 16 (FIG-1) is closed by the valve body 26. Thedrain valve piston 26 is formed with recesses 27 which, when the piston26 is in an extreme position, interconnect ducts 28, or 29,respectively, with the drain line 16. The connecting lines 12, 13 are influid communication with the ducts 28, 29, so that the pressure lines 8,9 of the reversible drive are likewise connected to the pressurelimiting valve unit 15.

Inserts 30, 31 are located within the unit 20 at either side of thedrain valve piston 26, forming therein charne bers 32, 33. Chambers 32,33 are formed with central bores 34, 35 into which extending projections36, 37 fit, the projections being formed on the drain valve piston 26.Chambers 32, 33 are not completely closed off by the projections 36, 37when the piston is in the central position shown in FIG. 2; aconstricted communication path exists between chambers 32, 33 and thespace facing the ends of the piston 26. Springs 40, 41 are additionallylocated within the chambers 32, 33 which act on perforated washers 42,43 in order to hold the piston in its central position. Bores 44, 45formed in the inserts 30, 31 interconnect chambers 32, 33, with ducts46, 47. Ducts 46, 47 form an interconnection between chambers 32, 33 anda main bore 48 in which a main piston 50 is located. Piston 50 is partof a precontrolled pressure limiting valve. When the pressure limitingvalve is closed, the two side faces 51, 52 respectively have pressureapplied thereto in chambers 53, 54, which corresponds to the pressure inchambers 32, 33 respectively.

Chamber 54 of bore 48 is connected by means of a duct 55 with a pilotvalve. The pilot valve itself includes a valve cone 57, loaded by aspring 56 which closes off duct 55. Set screw 58 permits adjustment ofthe highest operating pressure in lines 8, 9 by pre-setting or biassingspring 56.

The main piston 56, when in its closed position, separates the two lines12, 13 from each'other. The piston 50 can be formed as a valve, or,conversely, with a valve seat, as indicated at 60, FIG. 2.

The duct 47 is formed with a constriction 61. If valve cone 57 opens, asubstantial pressure drop will result in chamber 54, so that the mainpiston 50 will be rapidly opened due to pressure in chamber 53.

OPERATION Let it be assumed that the pressure side 8, corresponding toline 12, has higher pressure than lines 9, 13, due to loading of thereversible drive. The drain valve piston 26 is moved into its extremeright position, separating chamber 33 from duct 29, which is connectedwith line 13. Simultaneously, duct 29 is connected to drain line 16.Movement of piston 26 to the right clears opening 34 of chamber 32, sothat high pressure in chamber 32 will build up and be transferred overbore 44 to duct 46 and in chamber 53, opposite piston 50.Simultaneously, the pressure is transmitted through an axial bore 62formed in piston 26 into chamber 33 from where it can be transmittedover bore 45 into duct 47, passing through constriction 61. From duct47, high pressure is applied to fluid in chamber 54, which is alsoapplied over line 55 to valve body 57. As. can be seen, both chambers 53as well as 54 will have the same pressure applied as that in line 12.

If the higher pressure is at the pressure side 9, that is, connected toline 13, then the drain valve piston 26 is moved to the left (FIG. 2).Direct communication will be established between duct 29 and chamber 33.Chamber 32 likewise will have higher pressure applied thereto throughduct 62 formed in piston 26. Thus, regardless of the position of thedrain valve 26, the two chambers 53, 54 will have the higher pressureacting thereon.

If the higher pressure reaches the limiting pressure, to which the pilotvalve is set, then the cone 57 is lifted off its seat. Due to thepresence of constriction 61, a pressure drop will occur in chamber 54,moving the main piston 50 (FIG. 2) to the right and establishing ahydraulic short circuit between lines 12, and 13. This arrangementoperates independently of the particular line which has higher pressureapplied thereto since, in any instance, movement of the drain valvepiston 26 in its extreme position will conduct the higher pressure tothe chambers 53, 54, the respective lower pressure duct 28, 29 beingconnected by notches orreliefs in piston 26 witl'rthe drain line 16Under normal operating conditions, the main piston 50 is held on itsseat 60 by a relatively weak spring 63.

FIG. 2 clearly shows that lines 12, 13 operate directly and interconnectdirectly with the main piston 50. The pressure in chambers 53, 54 and inline 55 is controlled by the drain line in such a manner that,independently of which line 12 or 13 carries the higher pressure, thehigher pressure is always applied to both chambers 53, 54 and to line55. g

The present invention has been illustrated in connection with areversible hydrostatic drive, particularly adapted toa reversiblehydraulic motor; the output of the motor may be rotary or linear.

Various changes and modifications may be made 1 within the inventiveconcept.

and the reversible motor the direction of movement of the motor beingdetermined by which one of the pressure lines is placed under pressure;

a drain connection (16) for hydraulic fluid for the line not underpressure and returning fluid to said source (3);

a controllable pressure limiting valve to limit the pressure in the highpressure line interconnecting the pump and the motor to a controlledvalue, said controllable pressure limiting valve comprising a mainpiston (50);

connection means (12, 13) connecting hydraulic pressure from both saidpressure lines (8, 9) to said main piston (50);

a settable pilot valve unit (56, 57);

a connecting line (47) connecting fluid to said settable pilot valveunit (56, 57);

a drain valve (25, 26) having a movable drain control piston (26)connecting the connecting line (47) to that one of said connecu'on meansand hence said pressure line whichis under higher pressure than theother; and

a pair of interconnecting lines (46, 47) leading to opposite sides (51,53; 52, 54) of the main piston (50) and controlled by the drain controlpiston (26) of the drain valve (25, 26) to permit interconnection ofboth sides of the main piston with that one of the I pressure lines (8,9; 12, 13) which carries the higher pressure.

2. Drive according to claim 1, wherein the interconnecting line (47)applying fluid to the pilot valve (56, 57) includes a constricting choke(61).

3. Drive according to claim 1, wherein a pair of chambers (32, 33) areprovided connected to the interconnecting lines (46, 47) controlled bythe control piston (26) of the drain valve (25, 2.6);

and spring means (40, 41) are provided acting on the drain controlpiston (26) of the drain valve and located in said chambers (32, 33).

4. Drive according-to claim 3, wherein the drain control piston (26) islocated to open one of the chambers (32, 33) and close the other whenmoved into an ex- 6 trerne position (e.g.: FIG- 2,- right; 32 closed, 33open) to interconnect the respective one of the interconnecting lines(46) over the-open chamber (32) directly with the pressure side 1-2) ofthe connecting means (12, 13) carrying the-higher pressure;

said drain corittblbistoh (26) being formed with an axial bore (62'-)*'to' interconnecting the other one of the connecting-line's ('47)indirectly over said axial bore andthe' other chamber (33) with thepressure side of theconnecting means carrying the higher pressure(8,12).

5. Drive according to claim 4, wherein said main piston is located in amain piston bore (48);

and said main piston bore (48) is connected to both said connectingmeans (12, 13), the piston separating said connecting means when thepressure at opposite faces thereon is in balance and effecting a shortcircuit connection between said connecting means when the pressure atopposite faces thereon is unbalanced due to overpressure released by thepilot valve unit (56, 57).

6. Drive according to claim 4, further .comprising means (28, 29)interconnecting the connection means (12, 13) connecting hydraulicpressure from said pressure lines'(8, 9) to opposite sides of said drainvalve piston (26) when the piston is centered, said drain valve pistonbeing formed with means (27) intermediate its ends effectingcommunication between the pressure line carrying the lower pressure withsaid drain connection (16).

7. Drive according to claim 6, wherein; said means (28, 29)interconnecting the connection means (12, 13) and connecting hydraulicpressure from said pressure lines to opposite sides of said drain valvepiston (26); said connection means (12, 13); the means (27 effectingcommunication formed on the drain valve piston; and said drain (16) haveessentially the same fluid carrying capacity.

8. Drive according to claim 1, comprising a housing (20, 21, 22), saidhousing being formed with a drain valve bore (25), said drain controlpiston (26) being located in said drain valve bore;

a pair of chambers (32, 33) at each side of said drain valve bore andcommunicating therewith;

means (62) interconnecting said chambers;

means (40, 41) acting on and centering said drain control piston (26) insaid bore;

said housing being formed with a main piston bore (48), said main piston(50) being located in said main piston bore, one side of said mainpiston communicating with said pilot valve unit (56, 57); and means (28,29) interconnecting the connection means (l2, l3) connecting hydraulicpressure from said pressure lines (8, 9) to opposite sides of said drainvalve piston (26) when the piston is centered, said drain valve pistonbeing formed with means (27) intermediate its ends effectingcommunication between the pressure lines carrying the lower pressurewith said drain connection (16).

9. Drive according to claim 8, wherein the interconnecting line (47applying fluid from the chamber (33) to the main piston bore (48)terminating at the side face (52, 54) of the main piston (50) whichcommunicates (55) with the pilot valve (56, 57) is formed with a chokeconstriction (61);

and said main piston bore (48) is connected to both said connectingmeans (12, 13), the piston separat- 11. Drive according to claim 10,wherein said single duct element is formed with a constriction (61).

12. Drive according to claim 8, wherein said housing is formed with aduct (47) connecting one of the chambers (33) with said main piston bore(48) and terminating therein at a side of the face of the main piston(50), said duct forming both the connecting line connecting fluid to thesettable pilot valve unit (56, 57) and one of said pair ofinterconnecting lines (46, 47).

1. Hydrostatic reversible drive comprising a source of hydraulic fluid(3) and a pump (1) supplying hydraulic fluid under pressure; areversible hydraulic motor (10); pressure lines (8, 9) interconnectingthe pump (1) and the reversible motor (10), the direction of movement ofthe motor being determined by which one of the pressure lines is placedunder pressure; a drain connection (16) for hydraulic fluid for the linenot under pressure and returning fluid to said source (3); acontrollable pressure limiting valve (15) to limit the pressure in thehigh pressure line interconnecting the pump and the motor to acontrolled value, said controllable pressure limiting valve comprising amain piston (50); connection means (12, 13) connecting hydraulicpressure from both said pressure lines (8, 9) to said main piston (50);a settable pilot valve unit (56, 57); a connecting line (47) connectingfluid to said settable pilot valve unit (56, 57); a drain valve (25, 26)having a movable drain control piston (26) connecting the connectingline (47) to that one of said connection means, and hence said pressureline which is under higher pressure than the other; and a pair ofinterconnecting lines (46, 47) leading to opposite sides (51, 53; 52,54) of the main piston (50) and controlled by the drain control piston(26) of the drain valve (25, 26) to permit interconnection of both sidesof the main piston with that one of the pressure lines (8, 9; 12, 13)which carries the higher pressure.
 2. Drive according to claim 1,wherein the interconnecting line (47) applying fluid to the pilot valve(56, 57) includes a constricting choke (61).
 3. Drive according to claim1, wherein a pair of chambers (32, 33) are provided connected to theinterconnecting lines (46, 47) controlled by the control piston (26) ofthe drain valve (25, 26); and spring means (40, 41) are provided actingon the drain control piston (26) of the drain valve and located in saidchambers (32, 33).
 4. Drive according to claim 3, wherein the draincontrol piston (26) is located to open one of the chambers (32, 33) andclose the other when moved into an extreme position (e.g.: FIG. 2,right; 32 closed, 33 open) to interconnect the respective one of theinterconnecting lines (46) over the open chamber (32) directly with thepressure side (12) of the connecting means (12, 13) carrying the higherpressure; said drain control piston (26) being formed with an axial bore(62) to interconnecting the other one of the connecting lines (47)indirectly over said axial bore and the other chamber (33) with thepressure side of the connecting means carrying the higher pressure (8,12).
 5. Drive according to claim 4, wherein said main piston is locatedin a main piston bore (48); and said main piston bore (48) is connectedto both said connecting means (12, 13), the piston separating saidconnecting means when the pressure at opposite faces thereon is inbalance and effecting a short circuit connection between said connectingmeans when the pressure at opposite faces thereon is unbalanced due tooverpressure released by the pilot valve unit (56, 57).
 6. Driveaccording to claim 4, further comprising means (28, 29) interconnectingthe connection means (12, 13) connecting hydraulic pressure from saidpressure lines (8, 9) to opposite sides of said drain valve piston (26)when the piston is centered, said drain valve piston being formed withmeans (27) intermediate its ends effecting communication between thepressure line carrying the lower pressure with said drain connection(16).
 7. Drive according to claim 6, wherein: said means (28, 29)interconnecting the connection means (12, 13) and connecting hydraulicpressure from said pressure lines to opposite sides of said drain valvepiston (26); said connection means (12, 13); the means (27) effectingcommunication formed on the drain valve piston; and said drain (16) haveessentially the same fluid carrying capacity.
 8. Drive according toclaim 1, comprising a housing (20, 21, 22), said housing being formedwith a drain valve bore (25), said drain control piston (26) beinglocated in said drain valve bore; a pair of chambers (32, 33) at eachside of said drain valve bore and communicating therewith; means (62)interconnecting said chambers; means (40, 41) acting on and centeringsaid drain control piston (26) in said bore; said housing being formedwith a main piston bore (48), said main piston (50) being located insaid main piston bore, one side of said main piston communicating (55)with said pilot valve unit (56, 57); and means (28, 29) interconnectingthe connection means (12, 13) connecting hydraulic pressure from saidpressure lines (8, 9) to opposite sides of said drain valve piston (26)when the piston is centered, said drain valve piston being formed withmeans (27) intermediate its ends effecting communication between thepressure lines carrying the lower pressure with said drain connection(16).
 9. Drive according to claim 8, wherein the interconnecting line(47) applying fluid from the chamber (33) to the main piston bore (48)terminating at the side face (52, 54) of the main piston (50) whichcommunicates (55) with the pilot valve (56, 57) is formed with a chokeconstriction (61); and said main piston bore (48) is connected to bothsaid connecting means (12, 13), the piston separating said connectingmeans when the pressure at opposite faces (51, 53; 52, 54) is in balanceand effecting a hydraulic short circuit connection when the pressure atopposite faces thereof unbalances due to overpressure being relieved bythe pilot valve (56, 57), immediate balance of pressure being inhibitedby the constricting choke (61).
 10. Drive according to claim 1, whereinsaid connecting line (47) connecting fluid to the settable pilot valveunit (56, 57) and one of said pair of interconnecting lines (46, 47) areformed as a single duct element (47).
 11. Drive according to claim 10,wherein said single duct element is formed with a constriction (61). 12.Drive according to claim 8, wherein said housing is formed with a duct(47) connecting one of the chambers (33) with said main piston bore (48)and terminating therein at a side of the face of the main piston (50),said duct forming both the connecting line connecting fluid to thesettable pilot valve unit (56, 57) and one of said pair ofinterconnecting lines (46, 47).